1. Field of the Invention
The present invention relates to a maintenance method for subscriber lines of a broadband network termination (hereinafter celled a B-NT) apparatus in an asynchronous transfer mode permanent virtual connection (hereinafter called an ATM PVC) switching System, and in particular, to an improved fault management method for subscriber lines of a B-NT in an ATM PVC switching system which is designed to perform a switching function with respect to a virtual path (VP).
2. Description of the Conventional Art
Generally, an ATM PVC switching system which performs a switching function with respect to the virtual path unit and does not provide a signaling capability is disposed in an initial B-ISDN public network. The B-NT apparatus of a subscriber network of B-ISDN includes an apparatus for only performing a virtual channel (VC) switching function without concurrently performing a VP/VC switching function. The subscriber line is not directly connected to an ATM switching system and is mainly connected to the B-ISDN public network through the B-NT apparatus.
Since the B-ISDN is capable of providing various high speed and broadband services compared to a conventional public switched telephone network (PSTN), a public switched data network (PSDN), and an integrated service digital network (ISDN), it is very important to continuously provide with a high quality service to subscribers.
There are known conventional maintenance methods for subscriber lines of the B-NT in the ATM PVC switching system.
[Prior art 1]
U.S. Pat. No. 5,060,226, "Telecommunications Network Test System", Oct. 22, 1991, U.S.
[Article 1]
Rainer Handel, Manfred N. Huber, Stefan Schroder, "ATM Network: Concepts, Protocols, Applications", Addison-Wesley, 1994, pp. 129-133.
[Article 2]
ITU-T Rec. I.610, "B-ISDN Operation and Maintenance Principles and Functions", Geneva, Switzerland, 1994.
[Article 3]
Syephen C. Farkouh, "Managing ATM-based Broadband Networks", IEEE Comm. Magazine, May 1993.
[Article 4]
Jon Anderson, Laurent Hue, Lue Le Beller, "Operations Standards for Global ATM Network; Network Element view", IEEE Comm. Magazine, December 1996.
[Article 5]
ATM Forum Technical Committee Network Management Working Group, "M4 Interface Requirements and Logical Element View", December 1996.
A. A subscriber line test of a digital communication network.
According to the prior art 1, the subscriber line test of the digital network is performed by using a loopback method in the telecommunication line test system. In the master test unit, a test data is generated, and the generated test data is carried on a loopback message and then is transmitted to a remote unit. In the loopback mode, all the test data echoed back to master unit is compared and analyzed for errors using established B.E.R.T (Bit Error Rate Test) techniques. However, the prior art 1 is directed to a subscriber line test method which may be adapted to a digital communication network such as an ISDN. However, the prior art 1 can not be adapted to a subscriber line maintenance method with respect to the B-ISDN.
B. An operation, administration and maintenance (OAM) mechanism for the B-ISDN.
The ATM PVC switching system is capable of performing an OAM function of an ATM layer as far as the B-NT which is an end point of an F4 flow in the OAM flow based on an ITU-T I.610 of the articles 1 and 2. Therefore, on the assumption that the B-NT which performs the VC switching function is connected to the ATM PVC switching system, and a subscriber is connected to this B-NT, the ATM PVC switching system can not directly perform the OAM function with respect to a subscriber line (Sb interface) of the B-NT.
C. A method for using a loopback OAM cell
According to an ITU-T I.610 recommendation in the article 2, there are described the OAM principles and functions of the B-ISDN network. According to the ITU-T I.160, OAM loopback cells are used to verify part of or the complete end-to-end connection. This cell includes instructions as to where it should be looped, and does not effect user data. Cells may be looped within a local ATM network, across an intermediate network, or at a distant location. Therefore, this loopbacks simply allows the administrator to verify connectivity, localize faults.
D. A method for using a VC.sub.-- AIS message
In the articles 3 and 4, the B-NT which performs a VC switching function transmits a virtual channel--alarm indication signal (hereinafter called VC-AIS) to a downstream point of the virtual channel connection (VCC) when a fault is detected in a subscriber line. Namely, in all the apparatuses disposed in a downstream of a VC connection point, the VC-AIS is received, whereby it is possible to recognize that a fault is occurred in the Sb interface. However, since the ATM VP switching system performs only a VP switching function, it is impossible to recognize a VC.sub.-- AIS message. Therefore, in the ATM VP switching system, it is impossible to recognize the fault generated in subscriber lines of the B-NT.
E. A method for using an integrated network management system.
According to the network management system for a B-ISDN recommended in an ATM Forum Network Management WG (Working Group) disclosed in the article 5, the network management of a private network is managed by a private network management system, and the network management for a public network is managed by a public network management system. The management information exchange between the private network management system and the public network management system is performed by an M3 interface. Namely, The management information exchange between the ATM PVC switching system disposed in the public network of the B-ISDN and the B-NT apparatus disposed in the private network is performed by only the M3 interface. However, it may take long time for building the network management systems of the public network and private network of the B-ISDN and exchanging the management information therebetween. In addition, the above-described method is expensive compared to the method of directly maintaining the subscriber line of the B-NT apparatus in the ATM switching system.
According to the articles 1, 2, 3 and 4, it is impossible for the ATM PVC switching system to directly perform the OAM function with respect to a subscriber of the B-NT which performs the VC switching function.
In addition, according to the article 5, it may take long time for building the network management systems of the public network and the private network of the B-ISDN and exchanging the management information therebetween. In addition, the above-described method is expensive compared to the method of directly maintaining the subscriber line of the B-NT apparatus in the ATM switching system.